Project Summary/Abstract The quality and quantity of dietary lipid is important to many facets of human health. The ingestion of exogenous lipid has downstream effects on metabolically active tissues, such as the liver and the gastrointestinal (GI) tract. Many aspects of lipid transport and metabolism in the liver and GI tract are known, however the intracellular trafficking of lipids in these tissues, and the ramifications of that transport, are not fully understood. These studies will focus on the liver-fatty acid binding protein (LFABP), which is highly expressed in both the small intestine (SI) and the liver. Traditionally, LFABP has been considered to be a protein that is integral for lipid processing, assisting in the uptake and intracellular transport of lipid. Our recent studies have demonstrated that ablation of LFABP (LFABP-/-) in high fat (HF) fed mice results in dramatic effects on body weight and body composition when compared to wild-type (WT) mice. Interestingly, although HF fed LFABP-/- mice are markedly obese and hyperphagic, they display a metabolically healthy obese phenotype (MHO), with improved exercise performance and normal glucose tolerance. Studies performed in LFABP-null mice so far have only used global knock out mice, thus it is unknown if the dramatic changes in these mice are due to ablation of LFABP in the intestine, liver, or both tissues. Our recent studies have also demonstrated that HF fed LFABP-/- mice have elevated mucosal levels of the endocannabinoids (ECs), 2-arachidinoylglycerol and anandamide, which may contribute, in part, to the observed whole-body phenotype. Additionally, other groups have demonstrated that LFABP is able to interact with peroxisome-proliferator activated receptor alpha (PPAR?), indicating that LFABP may play a role in whole-body energy balance by altering the activation of this transcription factor. Based on these observations, our aims are to 1) determine the tissue-specific contributions of intestinal-LFABP and liver-LFABP to the MHO phenotype that has been observed in whole-body LFABP-/- mice; and 2) determine if LFABP acts as a lipid sensor and chaperone, facilitating the movement of lipid ligands to alter signal transduction and the activity of transcription factors. The proposed studies will use conditional knock out (cKO) LFABP mice generated via the CRISPR/Cas9 system, providing new information on the role that LFABP plays in regulating whole body energy homeostasis.